Exemplary embodiments of the present invention relate to a method for determining position data of a target object in a reference system from an observation position at a distance therefrom. Exemplary embodiments of the present invention further relate to a method for guiding an airborne weapon system to a target object and for aiming a weapon at the target object.
Many different operational forces may be present at various locations in the vicinity of a target area. The integration of information obtained from these distributed operational forces concerning the target area is necessary for situation assessment, and forms the basis for a coordinated response by these operational forces. Precise and unambiguous target data play a significant role in this regard.
Frequently, ground forces have already advanced near a target, and request air support. Coordination of an operation involving such forces spread out over a local area requires precise information concerning the target location. The most accurate position data of the target object which are necessary for this purpose may be obtained by operational forces which are already in the vicinity of the target. However, the position data of the target object obtained in this manner are initially only relative position data between the position of the target and the position of the observer.
One known option for guiding a deployed weapon, for example a missile, to a target is for the observer to illuminate the target, using a suitable device, and for the airborne missile to seek and approach the coded illuminated point. A major disadvantage of this method is that the observer may be revealed by the active illumination, which must necessarily be maintained for a certain period of time. In addition, this method is difficult to carry out in highly built-up areas due to a large number of obstructions and the resulting shadows from buildings.
Another known option for guiding a missile to a target is to use devices for determining geographical position data, for example satellite navigation devices, compasses, and maps, to ascertain the geographical position data of the target object and guide the missile to the target coordinates thus ascertained. However, such a determination of the geographical position data does not always meet the accuracy requirements necessary for a precise attack. In particular when civilian buildings and facilities are in the vicinity of the target object, the accuracy of the geographical position data determined in this manner is not sufficient to avoid inflicting collateral damage. Especially in urban areas or other densely populated regions, the slightest errors in determining the position data of the target object may have devastating consequences. The unambiguous and precise determination of the position data of the target object, for example a building from which the enemy is firing on forces, which is required for this operation scenario demands extremely high precision, which is not achievable from a safe distance using the means currently known.
Exemplary embodiments of the present invention provide a method for determining the position data of a target object from an observation position at a distance therefrom, which allows the position data of the target object to be precisely determined and the target to be unambiguously defined so that the target may also be quickly and clearly identified from a location other than the observation position, for example from an airborne missile.
Exemplary embodiments of the present invention involve:
a) Providing a three-dimensional reference model of the surroundings of the target object, the model including geographical location data;
b) Matching an image of the target object and its surroundings, resulting from the observation position for an observer, with the reference model; and
c) Determining the position data of the sighted target object in the reference model as relative position data with respect to known location data of the reference model.
Thus, according to an exemplary method of the invention, a shared three-dimensional reference model of the surroundings of the target object is provided to the observer. This three-dimensional reference model is also available to the airborne weapon. Using the above-mentioned steps of the method according to the invention, the observer is able to identify the target object in the three-dimensional reference model and define its position in this reference model. Based on the relative position data of the target object in the three-dimensional reference model defined in this way, the target object may be unambiguously identified from any other direction, and the weapon that is approaching from a given direction is able to unambiguously find and precisely strike the target object. The absolute positional accuracy of the three-dimensional reference model plays only a minor role, and only needs to be great enough that the association between the three-dimensional reference model and the scene that is modeled by an imaging device of the observer or the airborne weapon is possible. The use of relative position data of the target object in a reference system containing the reference model allows a reliable target definition and target address solely on the basis of the particular recorded image and the reference model, without having to precisely determine the absolute geographical position data of the target object, of the observer, and, for engagement of a target, also of the weapon.
One advantageous refinement of the method according to the invention involves the reference model provided in step a) being obtained from aerial photographs and/or satellite photographs of the target object and its surroundings. The reference models may be created in various ways. One option is photogrammetric measurement of high-resolution aerial photographs; another option is to carry out a three-dimensional reconstruction of the reference model based on image sequences recorded by reconnaissance aircraft, for example.
Alternatively or additionally, radar or LIDAR measurements of the target object and/or its surroundings may be used to obtain the reference model provided in step a).
In one advantageous embodiment of the method according to the invention, the image of the target object and its surroundings is matched to the reference model in step b) in the following substeps:
b1) Creating a three-dimensional line model from the three-dimensional reference model;
b2) Projecting the line model into the image of the target object and its surroundings recorded by an imaging device, based on a rough position and location hypothesis;
b3) Matching the lines of the three-dimensional line model with line segments extracted from the image line; and
b4) Computing a correction of the position and location hypothesis based on the match;
whereby the correction determined in step b4) is taken into account in determining the position data of the target object in step c). The image of the target object and its surroundings recorded from the observation position using a camera, for example, is matched to the three-dimensional reference model of the recorded scene. Based on this match, correction factors are computed for the position and location hypothesis, allowing the position and the location of the camera, i.e., of the observation position, to be accurately determined.
According to this advantageous refinement of the method according to the invention, first a three-dimensional line model is created in order to obtain a linear three-dimensional reference model. For the observer and the seeker head of an airborne missile, these lines form the basis for the positioning and location of the observer's own observation position. In addition to the three-dimensional reference model and the recorded camera image from the observation position, i.e., the camera image sequence, additional surroundings data may be entered for a rough initial position and location hypothesis. These surroundings data and additional data may be ascertained, for example, using a compass and satellite navigation system, or, in the case of a missile, via an integrated satellite navigation system and/or inertial navigation system.
In the method according to the invention for determining the position data of the target object based on the location data of the reference model in step c), it is also advantageous for the following substeps to be carried out:
c1) Determining the geographical position data of the observation position;
c2) Determining the position data of the target object relative to the position data of the observation position;
c3) Ascertaining the relative position data of the target object in relation to the reference model.
By ascertaining the relative position data of the target object in relation to the reference model according to these steps, an accurate relative position of the target object in the reference model may be easily defined using the position data of the observation position, determined by a satellite navigation device, for example, and the reference model, as well as the correction data determined in step b).
It is advantageous when the position data of the target object relative to the position data of the observation position are determined in step c2) by carrying out a distance measurement, preferably a laser range finding measurement, that is directed to the target object from the observation position, whereby the direction and the distance between the observation position and the target object ascertained in the distance measurement are used for determining the position data of the target object.
Alternatively, the position data of the target object based on the location data of the reference model in step c) may be determined in that the imaging device, which is located at the observation position, defines a virtual sight beam which corresponds, for example, to the optical axis of the imaging device, and the coordinates of the target point in the reference model, which is imaged by this sight beam on the target object, are determined as position data of the target object.
Exemplary embodiments of the present invention further relate to a method for guiding an airborne weapon system to an target object and for aiming a weapon of this weapon system at the target object, the position data of the target object in a reference system first being determined as relative position data in a reference model according to one of the preceding claims, and the following steps then being carried out for guiding the missile:
aa) Recording an image of the target object and its surroundings, using an imaging device provided onboard the missile;
bb) Matching the image obtained in step aa) with the three-dimensional reference model;
cc) Determining the position data of the imaging device, and thus of the missile, relative to the position data of the target object; and
dd) Guiding the missile to the target object, using the position of the missile relative to the target object ascertained in step cc).
This flight guidance method likewise makes use of the information concerning the relative position of the target object in the reference model. The airborne missile, using its imaging device, views the target object and its surroundings from a different viewpoint than the observer at the observation position. Also in this flight guidance method, the image obtained from the imaging device is first matched to the three-dimensional reference model. Since the coordinates of the target object in the reference model, i.e., in the reference system, have already been ascertained by the observer, the position of the missile relative to the target object may be quickly and easily determined, and therefore the missile may be reliably and accurately guided to the target object.
The airborne weapon system can be an unmanned missile which is guided to the target object using the method.
Alternatively, the airborne weapon system may be an aircraft provided with at least one weapon, for example a combat helicopter, the weapon being directed at the target object using the method.
Preferred exemplary embodiments of the invention together with additional design details and further advantages are described and explained in greater detail below with reference to the accompanying drawings.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.